Governor



Jan. 2l, 1958 E. B. H EFT 2,820,443

GOVERNOR Y Filed Deo. 25, 1955 2 Sheets-Sheet l I 3 to 29 y 5 G y 9 2.3

I, l O l /Z J/ l// I l I l 0 l ff l Q 'l if; 5 2 /5 2 24 zr l/ HEP 9 4 G,y 2, f. l 22 F Z, 26 O f "9 l /2 l l l, 3l /7 /l /3 f 0 l/ l l I Il 7 MMg LM@ I fnl/entomf/don B. Heft, S29/wf 0^ /775 Attorney.

Jan. 21, 1958 Filed Dec. 25, 1955 E. B. HEFT 2,820,443

/GOVERNOR 2. Sheets-Sheet 2 F7 .3f 26 O G l l /2 a/ /f /3 /l Il] G 6H lf 2 C) 9 4 I 70 JUMP fnl/en 'o/f 570/027 B. Heft,

H/'s /4 Torr-ley United States Patent() GOVERNOR Eldon B. Heft, NorthEast, Pa., assigner to General Electric Company, a corporation of NewYork Application December 23, 1955, Serial No. 555,002

16 Claims. (Cl. 123-103) This invention relates to an engine governorand more particularly to a speed responsive fuel rate mechanism for agovernor applicable to a diesel electric locomotive engine.

With the advent of the diesel locomotive, various speed responsivegovernors have been designed to accelerate the diesel engine when extrapower is required to accelerate the train. These governors are lowinertia devices which respond quickly to speed signals from the engine.Thus, in the event of an increased power demand as indicated by adecrease in the engine speed signal, the governor supplies more fuel tothe engine to increase and maintain its speed. However, during suchengine acceleration, fuel may be supplied to the engine at a rategreater than the combustion rate. This excessive fuel rate invariablyresults in acceleration smoke and often results in damage to theinternal engine parts.

Therefore, an object of my invention is to provide a simple and reliablespeed responsive governor which prevents smoking by limiting the supplyof fuel to that required by the engine.

A further object is to provide a governor especially adapted to theengine acceleration characteristic for controlling the rate of supply offuel.

In carrying out my invention in one form, the governor is provided witha time delay means to match the inertia of the particular engine beingaccelerated. When acceleration is called for by a decrease in speed ofthe engine, the governor increases the supply of fuel to the engine at apredetermined rate. If an increase in the load in the engine causes apredetermined. engine slow down, the governor removes a portion of theload to provide for rapid increase of the engine speed.

Further objects an-d advantages of my invention will be betterunderstood by reference to the following detailed description and theaccompanying drawings. The features of novelty will be pointed out withparticularity in the claims annexed to and forming part of thisspecilication.

ln the drawings,

Fig. l is a vertical sectional View of my governor showing the mainoperating parts at the start of the acceleraion cycle;

Fig. 2 is a vertical sectional View of my invention dnring load controlacceleration;I

Fig. 3 is a vertical sectional view of my invention during the resetcycle; and

Fig. 4 is a fragmentary view showing modifications of my improvedgovernor.

Referring now to the drawings in which like numerals refer to similarparts, I have shown one embodiment of my invention in Fig. 1 wherein agovernor 1 is provided with an inlet port 2 which supplies a fluid underpressure to the hydraulic system of the governor from a pump or othersources not shown. When the speed of an engine 3 drops because ofoverloading, a solenoid 4 is lenergized by a signal from a tachometer 5.The solenoid 4 ICC is connected to move a valve member 6 to the positionshown in Fig. 1 to open the inlet port 2. This admits the fluid underpressure to a passage 7 which commutates through a port 8 with a piston9. At the same time, fluid pressure is applied from the passage 7through a needle valve 10 to another piston 11.

The pressure of the lluid admitted through the inlet port 2 issulllcient to move the piston 9 upward with the fluid above the piston 9passing out through a passage 12 and a port 13. Movement of the piston 9rotates a gear 14 and an attached shaft 15. The shaft 15 is connected atone end to an operating arm 18 which normally rests against a stopmember 19 and at the other end to a variable voltage tap or brush 20 ofa voltage divider or rheostat 21. A load control spring 22, having anend 23 connected to the stop member 19, is tensioned between the stopmember 19 and the shaft 15 to force the operating arm 18 against thestop 19. In order to allow a more rapid acceleration of the dieselengine 3, a load control means shown as the rheostat 21 is connected inthe generator exciter circuit (not shown) to reduce the excitation ofthe generator and thus the load on the diesel engine during theacceleration. I prefer that this occur only under a load controlcondition to be explained more fully below. In the particulararrangement l have shown, I prefer that the spring 22 starts to wind uponly after 80 p. s. i. hydraulic pressure is applied to the piston 9.Thus, it is readily apparent that the spring 22 biases the piston 9toward the position shown in Fig. l.

However, the piston 11 requires a fluid pressure of only 65 p. s. i. tostart the piston 11 moving downward against the bias of a spring 24 and80 p. s. i. to completely compress the spring 24. This movement of thepiston 11 rotates the gear 16 and the shaft 17 to rotate a stop meanssuch as a cam 25 at a speed dependent on the fluid pressure and theopening of the needle valve 10. Brush pressure under the piston 11 isreleased by an oil drain 27.

In operation, when the engine 3 is running at too low a speed and morepower is required, the valve 6 is moved upward by a signal from thetachometer 5 to admit uid `to force the piston 9 upward, rotating theshaft 15 to increase the fuel -by causing a counterclockwise rotation ofa cam follower lever arm 26. This rotation causes a shaft 28 to rotateand a fuel control valve arm 29 to move the fuel supply means orracks-30 toward the full fuel position until a cam follower 31 engagesthe cam stop 25. Thus, the piston 9 drives the fuel racks 30 through thelinkage 18, 19, 22, Z3, 26, 28, 29 when the cam follower 31 is notstopped by engagement of the cam 25.

When the cam follower 31 engages the cam 25, further movement of thepiston 9 is prevented by the tensioned load control spring 22 until thepressure in the passage 7 reaches 80 p. s. i., at which time the piston9 continues to move upward against the bias of the spring 22 therebyforcing the governor into load control by further compressing the spring22. This further compression of the spring 22 is shown in Fig. 2, wherethe opl erating arm 18 is moved clockwise enough to provide a engagesthe stop 19 as shown in Fig. 3.

through the needle valve 10, forcing the piston 11 down against thespring 24 and rotating the gear 16, the shaft 17 and the cam 25 at apredetermined rate. It should be noted that the area surrounding thespring 24 is provided With the oil drain 27 which prevents any leakageoil from collecting therein to provide a back pressure under the piston11. As the cam 25 rotates, the cam follower 31 will allow the fuelcontrol valve arm 29 to be moved to the left by the tensioned loadcontrol spring 22 thereby increasing the fuel admission to the dieselengine 3 at a predetermined rate. Thus, when the cam follower 31 engagesthe cam 25, the spring 22 is further tensioned by continued upwardmovement of piston 9 and engine speed is allowed to increase morerapidly because of the reducedload during load control. I prefer thatthis linkage be designed so that only a few degrees rotation of the stopmember 19 is required to drive the fuel racks 30 from idle to full fuel.

When the engine speed reaches a predetermined desired value, the valve 6will close the inlet port 2 (Fig. 2) in response to a signal from thetachometer 5. At this time With a gap between' the operating arm 18 andthe stop member 19, the load control spring 22 requires 8O p. s. yi.pressure to remain tensionediwhile the spring 24 requires only 65 to 80p. s; i. to be moved a full stroke. In order to increase the generatorvoltage to its normal value while maintaining' the desired engine speed,the spring 22 will unwind the' stored signal, returning the Apiston 9downward toward its normal unbiased position and transferring fluidthrough the passage 7 and thev needle valve 10 to move the piston 11' inthe downward direction. In' order to allow r'nov'e-V ment ofthe piston9'w'ithout creating a vacuum above it when the valve 6 is closed, Iprefer that the valve 6 allow a slight seepage from the inlet port 2 toenter the passage 12.

As the piston 11 is driven downward, the cam 25 ro' tates toward thefull fuel position as shown in Fig. 3.

At the same time, since only a few degrees rotation of the spring 22 isrequired to drive the fuel racks 30, the piston 9 and the shaft 15 willbe returned suiciently to allow the brush 20 of the rheostat 21 to bereturned from the load control position to the full excitation position.In order to maintain the speed of the engine nearly constant during therecovery from load control, the fuel as controlled by the cam 25 and theload as controlled by the rheostat 21 are increased at a proportionalrate, and the piston 11 stops at the time theope'rating arm 18 engagesthestop member 19.

When it is desired to reduce the engine speed' and reset the governor,an overspeed signal is provided by the tachometer and the valve 6 ismoved from the position shown in Fig. 2 downward to the position shownin Fig. 3. This increases the pressure in the line 12 by connecting theinlet port 2 thereto and reduces the pressure in the line 7 by openingan exhaust port 32. The piston 9 is moved downward by the pressure inthe line 12. At the same time, the piston 1-1 is forced upward by thespring 24 to force the uid out through the needle valves and 33. Theback pressure on the needle valve 33 forces a check valve ball member 34downward to open this valve and allow the passage of fluid therethroughand reset the governor.

By the use of my invention, the time required to advance the fuel racksfrom one position to another may be either linear or variable by propercontouring of the cam 25. Thus, the governor may be made' to operatesatisfactorily with any type of diesel engine. For instance, if a dieselengine tends' to smoke less during acceleration at medium speeds thanduring acceleration at high or low'speeds, the contour of the cam 25 canbe made to allow an acceleration or fuel increase in the range of themedium speeds more rapidly than at the high or low speeds.

Also with this simple hydraulic governor, the fuel advance rate may bevaried by adjusting the needle valve 10 to meet all operatingconditions. I prefer that the needle valve 10 be set to provide sloweracceleration for passenger locomotives thus completely eliminatingengine acceleration smoke. For moderate acceleration necessary forfreight service, the needle valve may be set at an intermediateposition. For switching service where rapid acceleration is essential,the needle valve should be opened more fully.Y

Also, with my invention the reset time can be adjusted by moving theneedle valve 33 depending upon the service required from the locomotive.

In many locomotive jobs the use of the locomotive is determined beforeit is built so that the adjustable features of the needle valves 10 and33 are not necessary. Also, it has been found that the temperaturerating in service in locomotives is such that the viscosity of the fluidpassing through the needle valves greatly affects the rate of ow..Therefore in Fig. 4 I have shown the valves 38 and 39 wherein a seriesof thin plates 4t) each containing a small axial orifice to accuratelylimit the flow of the hydraulic fluid to the specil fied amount asi thetemperature of the hydraulic fluid varies over a wide range.

These thin plates eliminate a relatively large area of the film which'forms a part of the orice in such devicesas needle valves. This nlm iseliminated mainly by the fact that the surface of the orifice is smallcompared to the area thereof while the surface involved in a needlevalveof the same capacity is much greater. Since the viscosity of this filmvaries with uid temperature, the setting of any needle valve is varied,causing variation in the control of the acceleration depending onthefluid temperature. Of course, it would be necessary to vary the numberof plates for a particular locomotive, putting in more plates for thepassenger locomotive, fewer plates for the freight locomotive, and theleast number of plates for the switcher locomotive, thus allowing theminimum of smoke for the passenger locomotive and a greater amount ofsmoke for the switcher locomotive where it is not as offensive to thecustomers of therailroad.

I have found that after the valve 6 closes the inlet port 2 as shown inFig. 2, it sometimes occurs that the valve 6-does not move to theposition shown in Fig. 3 as rapidly or for as long a period asdesirable. In order. to preventsmoking because of space between the cam25 and the cam follower 31, by allowing the spring 24 to force' alimited' amount of uid out the valve 42 when the fuel racks 30 have beenmoved to a position which reduces the fuel one or more steps or notches.This valve 42 will not effect a change in the setting of fuel racksbecause of the fact that with this modification the spring 24 isdesigned to provide less tension than would be necessary to move thefuel racks back when the cam 25 engages the cam follower 31 or to forceenough Huid into the line 7 to move the piston 9 and the fuel racks 30ahead when the cam 25 does not engage the cam follower 31.

While I have shown and described particular embodiments of my invention,modifications thereof will occur to those skilled in the art. Therefore,I intend by the appended claims to coverall such modifications as comewithin the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A governor for` regulating the acceleration of an engine comprising arst relatively high speed hydraulic operating means, a second hydraulicoperating means having a relatively low speed matching the accelerationof the engine, a .common control valvefor said operating means .arrangedfor operation in response to a decreaseuin the speed of the engine tocause movement of said operating means, driving means including anaarmate movement storage spring for connecting said first operatingmeans to a fuel supply means of the engine for operation to increase thesupply of fuel to the engine, movable stop means cooperating with saiddriving means to limit the movement of said driving means and of saidfuel supply means to a predetermined amount after which continuedmovement of said first operating means is stored in said spring, and adriving connection between said second operating means and said stopmeans for moving said stop means to provide for movement of said fuelsupply means by said spring.

2. A governor for regulating the acceleration of an engine comprising afirst relatively high speed hydraulic piston, a second hydraulic pistonhaving a relatively low speed matching the acceleration of the engine,means biasing said pistons to predetermined positions, a common controlvalve for said pistons arranged for operation in response to a decreasein the speed of the engine to cause movement of said pistons, a linkageincluding a movement storage spring for connecting said first piston toa fuel supply means of the engine for operation to increase the supplyof fuel to the engine, movable stop means coopera-ting with said'linkageto limit the movement of said linkage and of said fuel supply means to apredetermined amount after which continued movement of said first pistonis stored in said spring, and a driving connection between said secondpiston and said stop means for moving said stop means to provide formovement of said fuel supply means by said spring.

3. A governor for regulating the acceleration of an engine comprising arelatively high speed hydraulic operating means, a second hydraulicoperating means having a relatively low speed matching the accelerationof the engine, a common control valve for said operating means arrangedfor operation in response to a decrease in the speed of the engine tocause movement of both of said operating means, a linkage for connectingsaid first operating means to a fuel supply means of the engine foroperation of said fuel supply means to increase the supply of fuel tothe engine, said linkage including a spring for storing movement of saidfirst operating means, movable stop means cooperating with said linkageto limit the movement of said linkage and said fuel supply means to apredetermined amount after which continued movement of said firstoperating means is stored in said spring, and a driving connectionbetween said second operating means `and said stop means for moving saidstop means to provide for movement of said fuel supply means by saidspring.

4. A governor for regulating the acceleration of an engine comprising afirst relatively high speed hydraulic operating means, a secondhydraulic operating means having a relatively low speed matching theacceleration of the engine, a common control valve for said operatingmeans arranged for operation in response to a decrease in the speed ofthe engine to cause movement of both of said operating means, a linkagefor connecting said first operating means to a fuel supply means of theengine for operation of said fuel supply means to increase the supply offuel to the engine, said linkage including a spring for storing movementof said first operating means, movable stop means cooperating with saidlinkage, a driving connection between said second operating means andsaid stop means for moving said stop means to provide for movement ofsaid fuel supply means by said first operating means, and means forbiasing said second operating means and said stop means to apredetermined position in which said stop means limits the movement ofsaid linkage and said fuel supply means to a predetermined amount afterwhich continued movement of said first operating means is stored in saidspring.

5. A governor for regulating the `acceleration of an engine, comprisinga first means responsive to an engine speed signal for increasing thefuel supplied to the engine, ,a SGGOnd ineans cooperating with saidfirst means so as t prevent an increase in the fuel supply greater thana predetermined rate, hydraulic operating means connecting said firstand second means, and means connected to said first means to store saidsignal and to reduce the load on the engine while said signal is beingtransmitted to said second means by said hydraulic means.

6. A governor for regulating the acceleration of an engine, comprising afirst piston responsive to an engine speed signal for increasing thefuel supplied to the engine, a second piston cooperating with said firstpiston so as to prevent an increase in the fuel supply greater than apredetermined rate, hydraulic operating means connecting said first andsecond pistons, and means connected to said first piston to store saidsignal and to reduce the load on the engine while said signal is beingtransmitted to said second piston by said hydraulic means.

7. A governor for regulating the acceleration of an engine, comprising afirst means connected to a fuel supply means for increasing the fuelsupplied to the engine, a second means adapted to prevent an increase inthe fuel supply greater than a predetermined rate, hydraulic operatingmeans connecting said first and second means, a valve connected to admitfluid to said hydraulic means in response to a speed signal from theengine, load control means connected to said first means to store saidsignal from said first means and to reduce the load on the engine untilthis signal stored is hydraulically transmitted to said second means,and means connected to said hydraulic means for resetting said first andsaid second means.

8. A governor for regulating the acceleration of an engine, comprising afirst piston connected to a fuel supply means for increasing the fuelsupplied to the engine, a second piston connected to a cam operatorhaving a cam contour adapted to engage the connection between said firstpiston and said fuel supply means to prevent an increase in the fuelsupplied greater than a predetermined rate, hydraulic operating meansconnecting said first and second pistons, a valve connected to admitfluid to said hydraulic means in response to a signal from the engine,load control means connected to said first piston to be energized bymovement of said first piston and to reduce the load on the engine untilsaid first piston is returned to a predetermined position and means forresetting said first and said second pistons.

9. A governor for regulating the acceleration of an engine comprising, afirst piston, connections connecting said first piston to a fuel supplymeans for increasing the fuel supplied to the engine, a second pistonconnected to a cam operator having a cam contour adapted to engage saidconnections to prevent an increase in the fuel supplied greater than apredetermined rate, a hydraulic system connecting said first and secondpistons, a valve connected to admit fluid under pressure to saidhydraulic system and adapted to be energized by a speed signal fromA theenginewhereby fuel to the engine is increased in response to saidsignal, a fiuid restriction connected in said hydraulic system to retardthe movement of said second piston, a load control spring connected tosaid first piston to be energized by movement of said first piston, aload control means operably connected to said first piston to reduce theload on the engine until said first piston is returned to apredetermined position and means connected in said hydraulic system forresetting said first and said second pistons.

l0. A governor for regulating the acceleration of an engine, comprisinga first piston, a connection connected between a fuel supply means andsaid first piston for increasing the fuel supplied to the engine inresponse to movement of said first piston, a second piston, a camconnected to said second piston, said cam being adapted to engage saidconnection between said first piston and said fuel supply means toprevent an increase in the fuel supplied greater than a predeterminedrate, a hydraulic system connecting said first and second pistons, avalve connected to admit fluid under pressure to said hydraulic asaoaassystem and adapted to be energized by av speed'signal from the enginewhereby fuel to the engine is increased, a needle'valve connected inisaid hydraulic system to retard the movement of said second piston, aload control spring connected in said connection to be energized bymovement of said first piston when said cam engages-said connection, aload control means operably connected to said first piston to reduce theload on the engine until said first piston is returned by said spring toa predetermined position and means connected in said hydraulic systemfor resetting said first and said second pistons.

11. A governor for regulating the acceleration of an engine, comprisinga first piston, a connection connected between a fuel supply means andsaid first piston for increasing the fuel supplied to the engine in`response to movement ofsaid first piston, a second piston, a` camconnected t said second piston, said cam being adapted to engage saidconnection betweenzsaid'rst piston and said fuel supply means toprevent` an increase in the fuel supplied greater than a predeterminedrate, a hydraulic system connecting said first and second pistons, avalve connected to admit fiuidr under pressure to said hydraulic systemand adapted to be energized by a speed signal from the engine wherebyfuel tothe engine s increased, a plate having a restricted axial orificetherein connected in said hydraulic system to retard the movement ofsaid second piston, a load control springY connected in said connectionto be energized by movement of said first piston' when said cam engageslsaidconnection, a load control means operably connected to said first'piston to reduce the load on the engine until' said first piston isreturned-by said spring to a predetermined position and means connectedin said hydraulic system for' resetting said first and said secondpistons.

12. A governor for regulating the accelerationY of an engine providedwith fuel racks, comprising a first piston, connections connectedbetween the fuel racks and said first piston for increasing the fuelsupplied to the engine in response to movement of said first piston, asecond piston, a cam connected to said second piston for engaging saidconnection to prevent an increase in the fuel supplied greater than apredetermined rate, a hydraulic system connecting said first and secondpistons, a valvc connected to admit fiuid under pressure to saidhydraulic system and adapted to be energized Iby a speed signai k` fromthe engine whereby fuel to the lengine is increased in response to saidsignal, a first needle valve connected in said hydraulic system toretard the Vmovement of said second piston in response to uid pressurein said system,

a load control spring connected to said first `piston to be energized bymovement of said first piston, said spring thereafter biasing said firstpiston toward its normal position to create a pressure in said hydraulicsystem suiiicient to drive said second piston and rotate'said cam, aby-pass line around said restricted plate, a check valve in said line toprevent iiuid flow therein to said second piston, and a second needlevalve connected in said line for controlling the reset period of saidsecond piston.

13. A governor for regulating the acceleration of an engine providedwith fuel racks, comprising a first piston. connections connectedbetween the fuel racks and said first piston for increasing the fuelsupplied to the engine in response to movementV of said first piston, asecond piston, a cam connected to said second piston for engaging saidconnection to prevent an increase in the fuel supplied greater than apredetermined rate, a hydraulic system connecting said first and secondpistons, a valve connected to admit iiuid under pressure to saidhydraulic system and adapted to be energized by a speed signal from theengine whereby fuel to the engine is increased in respouse to saidsignal, a first plate having a restricted axial orifice therein.connected in said hydraulic system to retard the movement of said secondkpiston in response to duid pressure in said system, a load controlspring connected to saidffirst piston to be energized by movement of'vsaid Afirst piston, said spring thereafter biasing said first pistontoward' its normal position to create a pressure in said hydraulicsystem .sufficient to drive said second Apiston and rotate said cam, aby-pass line around said restricted plate, a check valve in said line toprevent fiuid dow :therein to said second piston, and a second platehaving a restricted axial orifice connected in said line for controllingthe reset period of said second piston.

14. A governor for vregulating the acceleration of an engine providedwith fuel racks, comprising a first piston, connections connectedbetween the fuel racks and said piston for increasing the fuel ysuppliedto the engine in response to movement of said first piston, a secondpiston,

a contoured cam operably connected to said second pis-- ton for engagingsaid connections between said first pistonl and said fuel racks toretard the movement of said connections, a hydraulic system connectingsaid first and second pistons, a valve connected to admit fiuid underpressure to said hydraulic system and adapted to be energized by asignal from the engine whereby fuel to the engine is increased inresponse. vto the speed of the engine, a plurality of plates havingy arestricted axial orice therein connected'insaid.hydraulic system toretard the movement of said second piston in response to said pressure,a load control spring connected to said first piston for storing thesignal from said engine until the signal is hydraulically transmitted tosaid second piston, said spring being tensioned by movement of said rstpiston beyond the port where said camrengages said connections, saidtensioned .spring kdrivingly connected to said first piston whereby saidfirst piston drives said second piston to rotate said cam and allow anincrease in fuel supplied to the engine, a load control means operablyconnected to a said first piston to reduce the load on the engine untilsaid first piston is returned by said spring to said predeterminedposition, a line connected to by-pass said plates, and a check valve insaid line to allow fiuid flow in said line from said second piston forresetting said second piston.

15. A governor for regulating the acceleration of an engine providedwith a fuel rack, comprising a first piston, means for applying fluidpressure to said first piston, connections operatively connected betweenthe fuel rack and said piston, a second piston, a contoured cam operablyconnected to said second piston for engaging said connections to preventan increase in the fuel supplied greater than a predetermined rate, saidconnections being provided with a load control spring adapted to betensioned by movement of said first piston when said cam engages saidconnections, a hydraulic system connecting said first and second pistonswhereby said tension on saidv spring is transferred from `said firstpiston to said second piston, a restriction in said hydraulic systembetween said first and second pistons to retard the movement of saidsecond piston in response to said tension, means operably connected tosaid first piston tov reduce the load on the engine until said firstpiston is returned by said spring to a predetermined position', a fluidpressure line connected to by-pass said restriction, and a check valvein said line to allow fiuid fiow in said line from said second pistonfor resetting said second piston.

, 16. A governor for regulating the acceleration of an engine providedwith a fuel rack, comprising a first piston, means for applying fiuidpressure to said first piston, connections operatively connected betweenthe fuel rack and said piston, a secondpiston, a contoured cam operablyconnected to said second piston for engaging said connections to preventan increase in the fuel supplied greater than a predetermined rate, saidconnections being provided witha loadcontrol springadapted to betensioned by movement of said first piston when said camvengages saidconnectionsa hydraulic system connecting said first and second pistonswhereby said tension on said spring` is transferred from said firstpiston to said second piston, References Cited in the le of this patenta restriction in said hydraulic system between said rst and secondpistons to retard the movement of said sec- UNITED STATES PATENTS ondpiston in response to said tension, and means oper- Re- 23,490Alexanderson et al May 20I 1952 ably connected to said first piston toreduce the load on 5 2 685,871 Block Aug 10 1954 the engine until saidrst piston is returned by said spring 2721 072 Zuhn et al Oct 18' 1955to a predetermined position.

